Electronic security system



March 8, 1966 A. E. MARTENS 3,239,815

ELECTRONIC SECURITY SYSTEM Filed Nov. 15, 1962 3 Sheets-Sheet 1 FIG. I

To POWER H SOLENOID OR MOTOR L 42 FOR OPERATING THE LOCK INVENTOR. A LEXANDER E. MARTENS ATTORNEY March 8, 1966 A. E. MARTENS 3,239,815

ELECTRONIC SECURITY SYSTEM Filed Nov. 15, 1962 5 Sheets-Sheet 2 Panoramas e7 LOCK 68 To ALARM To Sounca OF 5| AC POWER 5s INVENTOR. 2 57 ALEXANDER ammcus'g AT T ORNE Y March 1966 A. E. MARTENS ELECTRONIC SECURITY SYSTEM 5 Sheets-Sheet 5 Filed Nov. 15, 1962 SINGLE OR PLURALITY u2 2 FZEnEMOZC G Q O FIG.5

FIG. 6

8 mm Cu INVENTOR. ALEXANDER EMARTENS BY 9 9 i;

A T TORNEY United States Patent 3,23),815 ELECTRONIC SECURKTY SYSTEM Alexander E. Martens, Greece, N.Y. (14 Kartes Drive N., Rochester, N.Y.) Fited Nov. 15, 1962, Ser. No. 237,888 6 Claims. (Cl. 340-149) This invention relates to a locking system and more particularly to an electronically compared master and key card locking system.

An electronic locking system can be adapted to readily provide an alarm in event of tampering with the lock, automatically unlock and open a door to permit entrance, or to initiate operation of various kinds of machinery, providing the proper identification is inserted in the system. A dual card system employing a master code on a master card located within a confidential or normally inaccessible area and a mating key card, simulating the master card, readily identifies the authorized carrier and permits entry when inserted in the proper slot. This type of a system permits a quick substitution of the master card and accordingly a change in the lock combination which is impractical with the conventional key system.

It is an object of this invention to provide a locking system which electronically operates in response to a suitable identifying code.

It is a further object of this invention to provide a fool-proof photo-electric locking system having a master coded card adapted for placing in a normally inaccessible or secret location and requiring a like coded key card to operate the locking system.

It is a further object of this invention to provide a photo-electric locking system having radiation sensitive elements to actuate an unlocking means or actuate an alarm in accordance with identity or lack of identity of the master and key cards.

The objects of this invention are accomplished by providing an electronically balanced photo-electric locking system. Any suitable source of electrical energy may be used to operate the system. The electric circuit includes a bridge circuit containing photo-electric elements which control current flow in response to radiation. A master photo'sensing unit is associated with one bank of the photo-electric elements and a single or a plurality of mating key photo-sensing units is associated with the other corresponding bank of photo-electric elements. A master card is inserted in the master photo-sensing unit which controls the current flow in the master photo-electric elements. A similar key code card which is to be carried by authorized personnel is inserted in the locking system to control the radiation impinging on the key photo-sensing elements and provides a balanced output of the circuit providing both the key and master cards are identical. A suitable unlocking device is electrically connected to the system to unlock the lock, providing the system remains balanced. If an unbalance exists the system automatically initiates an alarm and does not open the look. In this manner the cards may be given to authorized personnel and may be changed by the owner whenever desired.

The photo-sensing units may employ the polarization of light or complete obstruction of the light in predetermined areas by a card which is intermediate the source of radiation and the photo-sensitive cells. The card may be constructed in such a manner that the intelligence layer may be intermediate two covering layers to prevent a person from deciphering the code. It is also pointed out that the system could operate under the principle of invisible radiation which would further complicate deciphering the code on the card.

Additional advantages of the system will become apparent from the following detailed description of which the preferred embodiments are illustrated in the attached drawings.

FIG. 1 is a circuit diagram of the photo-electric locking system.

FIG. 2 is a modification of the circuit diagram of the photo-electric locking system.

FIG. 3 illustrates the photo-sensing units including the cards and the photo-electric elements.

FIG. 4 'is a modification of the photo-sensing unit having a different source of radiation and control of the radiation impinging on the photo-electric elements.

FIG. 5 is a card having perforations adapted for operation in the photo-sensing unit.

FIG. 6 is a modification of a card having dissimilar material which might be adapted for polarization of light to control transmission of light through the card.

FIG. 7 illustrates a construction where an intelligence layer is sealed intermediate the covering layers of the card.

FIG. 8 is a segment of the bridge circuit illustrating the electrical connections of the like elements illustrated in FIG. 3.

Referring to the drawings, FIG. 1 illustrates a version by which the system might be arranged. Any source of electrical energy would adapt itself readily to a system such as illustrated. The battery 1 provides power for the system. The battery 2 energizes the alarm system, however a single source of electrical energy (such as a power transformer operating from a power line) would be adequate to supply the whole system. The battery 1 is connected to ground on one side. The opposite side of the battery is electrically connected to the plurality of radiation sources 3, 4 and 5 on the master photo-sensing unit 6. A similar connection connects the radiation sources 7, 8 and 9 of the key photo-sensing unit 10. The sources of radiation might be any suitable lamp it visible light is used, or any suitable source radiating invisible light if this type of radiation is preferred in the system. The opposite sides of the filaments are connected to the control switch 11. The control switch It is actuated by the key card 12. As the key card 12 is inserted in the proper slot the switch 11 is closed connecting the one side of the filaments to ground and energizing the system. For the purpose of illustration only, the sources of radiation will be designated as lamps. The inventor does not, however wish to limit the source of radiation to any specific type of radiation but merely is using the term lamp to facilitate in the description of the invention. As the lamp 5 radiates it causes the photoelectric element 13 to actuate permitting the how of current through the solenoid 14. The energizing of the solenoid l4 closes the arm 15 to engage the contact 16.

The bank of photo-electric elements in the master photo-sensing unit are positioned in an array. The array might be limited to only a few elements or to a very complex array where the number is greatly increased in event that security dictates this type of a system. The master photo-sensing unit includes an element 17 intermediate the lamps 3, 4 and 5 and the bank of photoelectric elements. The master card 13 is inserted in the proper slot intermediate the element 17 and the bank of photo-electric elements. Inserting of the master card 18 has no immediate effect on the system but merely provides the code which must be later duplicated on the key card side of the bridge circuit. FIG. 4 illustrates a similar arrangement of the photo-sensing unit wherein the lamp 19 and reflector 20 radiate light on a diffusing plate 21. The plate 21 might also be a collimating means in directing the light toward the array 22 of photo-electric elements. The card 18 limits the transmission of the radiation to specific photo-electric elements in the array 22.

Referring again to FIG. 1 the array of photo-electric elements may be sensitive to a single wavelength or a plurality of wavelengths whichever is suitable. If each element were sensitive to a different wavelength of light it would further complicate the system and prevent the breakdown of the code under which the system would operate. For simplicity we will assume that all the lamps 3, 4 and 5 operate on the same wavelength. Assuming that the system is in operation which, of course, must be initiated by the inserting of the key card 12 and energizing the system through the switch 11. The radiation from the lamps 3, 4 and 5 is directed through the plate 17 and transmitted through a limited portion of the card 18 and impinges on each of the selected photo-electric elements in the array 22. The photo-electric element 23 is electrically connected through the solenoid 24 to the battery 1. The photo-electric element 25 is similarly connected through a like solenoid 26 to the battery 1. Each photo-electric element is electrically connected through a mating solenoid to the battery 1. The number and location of the particular photo-electric elements energized is controlled by the code in the card 18. -If light is transmitted through the card and impinges on the photo-electric element current is conducted through the photo-electric element controlled by this area on the card 18. Each of the solenoids in the bank of solenoids controls a single pole double throw switch. Solenoid 24 controls the switch 27 and solenoid 26 controls the switch 28 and likewise through the bank of solenoids and switches.

The key card photo-sensing unit is a similar arrangement or like parts simulating the master photosensing unit. The element 29 is positioned intermediate the lamps 7, 8 and 9 and the key card 12. This element might be a collimating element, a diffusing element, or polarizing element depending on which radiation principle is used in the system but would be similar to element 17. The array of photo-electric elements 30 receive radiation when the circuit is energized in accordance with the code on the card 12. The photo-electric element 31 controls the energization of the solenoid 32 and the photo-electric element 33 controls energization of its mating solenoid 34. Similar photo-electric elements actuate their mating solenoids in a manner similar to the master sensing unit. The solenoid 32 operates a single pole double throw switch 35 and the solenoid 34 operates a single double throw switch 36. The bank of switches operated by the solenoids provide a continuous circuit through the bank of switches so long as the opposing pairs of solenoids, such as the solenoids 24 of the master sensing unit and the solenoid 32 of the key sensing unit are simultaneously actuated. The same situation is also true if the corresponding pairs of solenoids are not actuated. If one of the pairs of solenoids however is actuated ad the other is not, there will not be a continuous fiow of current through the bank of switches 43, because the circuit will be opened, and the system will fail to operate the power solenoid for the motor to open the lock.

The bank of switches is connected on the right hand side to the battery 1. The left hand side of the bank switches is connected through the switch 37 to the solenoid 33 and to ground through the switch 11. Energization of the solenoid 38 draws the armature 39 to a contacting position with the contact 40 which in turn energizes the solenoid 41. Energization of the solenoid 41 operates the switch 42 and the motor for operating the lock.

In event that there is no continuity through the bank of switches 43 no current flows through the solenoid 33 and the armature 39 remains in contact with the contact 4-4. This in turn initiates an alarm.

Referring to FIG. 2 a modification of the circuit diagram is illustrated. The array of photo-electric elements have been reduced to six purely for simplification of the circuit. The source of power is an alternating current transformer, connected to a power line with a rectifier unit to provide a DC. current for a portion of the system. The system also operates on the principle that in case an unbalance exists in the electrical circuit responsive to dissimilar master and key cards an error signal is generated preventing the lock from opening and initiating an alarm.

The primary winding of the transformer 51 is connected to any suitable source of alternating current. Two secondary windings 52 and 53 are provided in the transformer 51. The winding 52 operates a bridge rectifier unit 54 including a capacitor 55. The rectifier unit is connected to the lamps 56 and 57 in the key photo-sensing unit as well as the lamps 58 and 59 in the master photosensing unit. The rectifier unit 54 also provides energy to the resistor 60 which operates with a sliding contact 61 connected to the solenoid 62. The capacitor 63 prevents spurious signals from actuating the solenoid 62. The output of the system is connected to delay circuits 66 and 67 to prevent momentary erroneous signals from actuating either the alarm or the motor. The solenoid 62 actuates the single pole double throw switch 64 and the single pole single throw switch 65.

The secondary winding 53 provides a source of energization for the master photo-sensing unit 68 and the key photo-sensing unit 69. The opposite ends of the winding 53 are connected to the photo-sensing units through a common connection. The connections establish a plurality of Wheatstone bridges which generate individual signals in event of an unbalance on any one of the bridges. The terminal 70 is connected intermediate the resistor 71 and 72 which are resistors of equal value. The terminal 73 on the opposite side of the winding 53 is connected intermediate the photo-electric elements 74 and 75 establishing a Wheatstone bridge circuit through connecting these four elements. Intermediate the resistor 71 and the photo-electric element 74 is a ground connection and intermediate the resistor 72 and the photoelectric element 75 is connected a rectifying element 76. In event of an unbalance in this bridge circuit a signal is generated causing current to flow through the solenoid 62, the resistor 77 and the rectifying element 76. The unbalance signal passing through the solenoid 62 energizes the solenoid and initiates an output signal causing the armature 78 and the armature 79 respectively to engage the contacts 80 and 81.

The photo-electric elements in the array 82 of the master photo-sensing unit 68 and the array 83 in the key photo-sensing unit 69 all operate in a similar manner. If mating photo-electric elements in each of the two arrays 68 and 69 are simultaneously energized no signal is generated on this particular bridge circuit. If, however an unbalance is present in the specific bridge circuit containing the mating two photo-electric elements a signal is generated and the solenoid 62 is energized creating an output signal. An amplifier may be connected to reccive the signal from the rectifying elements and with the output from the amplifier energizing the solenoid 62, if the signal is weak.

The actuation of the system is similar to FIG. 1 wherein a key card 84 is inserted in the proper slot closing the switch 85. Energization of the solenoid 62 causes the switch 65 to over-ride the switch 85. The lamps being energized direct light through the plates 86 and 87 to their proper array of photo-electric elements 69 and 63 respectively.

Capacitors 88 and 39 prevent spurious signals from actuating solenoid 62 and assist in more uniform operation of the circuit.

FIG. 3 illustrates photo-sensing units which might be used in a system of this type. Assuming the photo-sensing unit 93 to be the master photo-sensing unit and 91 to be the key photo-sensing unit. The plate 52 represents an electroluminescent device having electrical conductors 93 and 94 energizing the device. A uniform radiation is directed on a polarizing plate 95. A second polarizing plate 97 is positioned adjacent the array 96. The array 96 pictorially illustrates the array 22 in FIG. 1. The master card 9% has additional elemental areas. Means are provided for maintaining the direction of the light to the plurality of areas 75 etc., accordingly each segment controls a portion of a bridge circuit. An identical key photo-sensing unit 91 is positioned at an accessible point where the key card 99 may be inserted in the proper slot. The polarization plates 1'15 and 117 would "be oriented to control the plane of the polarization in the key photosensing unit. The card 99 must be identical with the master card 98 to provide the proper balance and output to actuate the lock circuit.

The cards 98 and 99 would be constructed similar to FIG. 6 wherein the area 100 would be polarized in one plane and the area 101 would be polarized a different plane. The sections are polarized in a desired plane of polarization. Area 102 having no polarization would permit direct transmission of light through the card. In this manner the code is imprinted on the master card and duplicated on the key card.

FIG. 5 illustrates a modification where perforations 103, 104 etc. are positioned in the card according to the code. The perforations may also be replaced with sections transparent to radiation while the remaining portion of the card is pervious to radiation. For purposes of secrecy the card illustrated in FIG. 7 is coated with a radiation transmitting material 105 and 105 not readily identifiable by the naked eye and may contain a camouflaged printing to prevent identification with the locking system. A card such as illustrated in FIG. 7 is carried by authorized personnel to provide a means for unlocking a system.

The card may also carry the fingerprint and name of the authorized person. An alignment tab would serve to prevent operating the circuit by inserting the card improperly in the slot. Also, a plurality of cards might be used whose combined code duplicates the master card code when inserted in the proper slot together.

FIG. 8 illustrates a segment of the circuit in FIG. 2 which forms one of the plurality of Wheatstone bridges. The photo-electric element 75 illustrated in the master photo-sensing unit of FIG. 3 would be the same element 75 in FIG. 2. The photo-lectric element M in FIG. 2 would be 74 in the photo-sensing unit 91 in FIG. 3. The resistors 71 and 72 would correspond to the same numbers in FIG. 2 thereby providing an elemental Wheatstone bridge.

The operation of the device will be described in the following paragraphs. Referring to FIG. 1 the master card 18 is positioned in a suitable slot within a normally inaccessible area, or a secret area. A similar slot is provided for the key card 12 near the locked are-a. The master array 22 of photo-sensitive elements are positioned adjacent to the master card 18 and are activated in response to the code in the card 18 as the system is energized. A similar array 30 of the key photo-sensing unit is positioned adjacent the card 12. The card 12 is a duplicate of the master card 18. The duplicate card 12 will activate the photo-electric elements in the array 30 corresponding to the mating photo-electric elements in the master array 22. Mating solenoids will actuate like switches in the bank of switches 43. In event both master and key cards are identical, all mating solenoids and switches will be actuated providing continuity through the bank switches d3 and the switch 37 to the solenoid 38. Energization of the solenoid switch 38 causes the armature 39 to engage the contact 49 which in turn energizes the solenoid 41. The solenoid 41 closes the switch 42 and supplies power for operating the door to the confined area such as a safe or vault.

In event that the key card 12 is not identical with the master card 13 an unbalance will be set up in the electrical 6 circuit breaking the continuity through the bank of switches 43. Likewise no current is supplied to the solenoid 38 and the armature 39 remains engaging the contact 44. The battery 2 supplies energy to initiate an alarm and the door 2 in the confined area is not opened.

Referring to FIG. 2 a similarly operating system is illustrated. The source of energization however is alternating current and provides a rectifier for direct current as well. The master card is inserted in a proper slot within a confined or secret area. The key card 84 which is carried by authorized personnel is inserted within the proper slot in the key photo-sensing unit. It the key card 84 is identical with the master card 116 all of the mating photo-electric elements provide a balance throughout the electrical circuit and no signal is generated and the solenoid 62 is not energized. The armature 78 of the single double throw switch 64 remains engaging the contact 111 which supplies energy to the delay circuit 67 which after a short delay energizes the mot-or for opening the door.

In event that the key card 84 is not identical with the master card 110 an unbalance signal is generated which flows through the solenoid 62 causing the armature 73 to engage contact 89. This energizes a delay circuit 65 and after a short delay initiates an alarm. Once the circuit is energized the switch 65 overrides switch 35 and if the key and master cards are not identical the alarm will operate, as retracting the key card will not de-enerize the circuit. This prevents tampering with the lock and give a fool-proof system.

Referring to FIG. 3 an electroluminescent device 92 is illustrated. The inventor does not wish to limit the type of radiation to any particular device but has merely illustrated more than one means for .the purpose of illustration. The radiation might be in the visible spectrum or the invisible spectrum. It is only necessary that the radiation activates the photoelectric elements in the photosensing unit. FIG. 3 illustrates a polarizing device which establishes at least one plane of polarization in the photosensing units.

The photo-electric elements might be diodes, resistors, transistors or any suitable light responsive elements. The photo-electric elements are suitably connected in a circuit providing a balance which is initially established by the master card and duplicated in the key card.

FIG. 4 illustrates a modification where a source of radiation might be collim-ated or diffused by a plate 21. It is important that the light be directed on the card 23. The card 23 controls the transmission to the array of photoelectric elements 22.

The device is illustrated and described and sets forth the preferred embodiment of the applicants invention. Other devices might be devised which would fall within the scope of the invention. The attached claims define the limits of the applicants invention.

I claim:

1. A locking system comprising, a plurality of electrically balanced bridge circuits connected to a source of electrical energy with each bridge circuit including pairs of photo-electric elements forming legs in said bridge circuit, a master photo-sensing unit including the first of photo-electric elements in said pairs forming one of said legs in said bridge circuit and radiation means directing radiation toward said photoelectric elements in said master unit, a key photo-sensing unit including the second of photo-electric elements in said pairs forming another of said legs in said bridge circuit and radiation means directing radiation toward said photo-electric elements in said key unit, a master code card including radiation transparent and radiation impervious areas defining a predetermined code received in said master photo-sensing unit optically intermediate said radiation means and said photoelectric elements, a key code card including radiation transparent and radiation impervious areas duplicating said master code card received in said key photo-sensing unit optically intermediate said radiation means and said photo-electric elements providing a balanced output signal from said bridge circuit in accordance with similar conducting of said pairs of said photo-electric elements in said circuit, an output circuit receiving a signal from said balanced circuits, said output circuit including means selectively initiating opening of a lock or initiating an alarm in accordance with comparative readings from said circuit.

2. A locking system comprising, an electronically balanced circuit including a plurality of bridge circuits connected to a source of electrical energy, photo-electric elements forming legs in said bridge circuits, a master photo-sensing unit including photo-electric elements forming one of said legs in said bridge circuits, a key photosensing unit including photo-electric elements forming the other of said legs in said bridge circuits, a source of radiation in each of said photo-sensing units directing radiation on said photo-electric elements, a master code card including radiation polarized and radiation nonpolarized portions defining a code received in said master photo-sensing unit intermediate said source of radiation and said photo-electric elements, a duplicate key code card including radiation polarized and radiation nonpolarized areas defining a like code received in said key photo-sensing unit intermediate said source of radiation and said photo-electric elements and providing a balanced output in said circuit in accordance with comparative electrical conductance of said pairs of photo-electric elements in said circuit, an output circuit receiving a signal from said balanced circuit including means selectively initiating opening of a lock or initiating an alarm in ac cordance with the comparative conductance in said balanced circuit.

3. A locking system comprising, a plurality of electrically balanced bridge circuits connected to a source of electrical energy, photo-electric elements in said circuits forming legs in said bridge circuits, a master photo-sensing unit including photo-electric elements forming one of said legs in said bridge circuits, a key photo-sensing unit including mating photo-electric elements forming another of said legs in said bridge circuits, a source of radiation in each of said photo-sensing units, a master code card received in said master photo-sensing unit having elemental areas defining a code controlling radiation on said photo-electric elements, a plurality of key code cards having combined elemental area layers defining a code duplicating said master code card and received in said key photo-sensing unit controlling radiation on said photoelectric elements to provide a balanced output from said circuit in accordance with conductance of said pairs of photo-electric elements in said circuit, an output circuit receiving a signal from said balanced circuit and including means selectively operating an alarm or operating a lock control.

4. An electronic locking system comprising, an electrically balanced circuit including a plurality of bridge circuits, a master radiation sensing unit including a radiation sensitive electrical element forming a first leg in each of said circuits, a key radiation sensing unit including a radiation sensitive electrical element forming a second leg in each of said circuits, a source of radiation in each of said units directing radiation on said radiation sensitive electrical elements, a master code card received Within said master unit positioned intermediate said source of radiation and said radiation sensitive elements, a key code card received in said key unit positioned intermediate said source of radiation and said radiation sensitive elements, radiation pervious and impervious portions in each of said cards defining like identification codes controlling impingement of radiation on said radiation sensitive elements and generating a balance signal responsive to an electrically balanced condition in said circuit, an actuating switch connected to said balance circuit and operated by said key card for energizing said circuit, an over-riding switch connected to said circuit for actuation in response to an unbalance signal from said circuit only if an unbalanced condition exists in the circuit to maintain circuit energization for generating an alarm.

5. A locking system comprising, an electrically balanced circuit including, a plurality of Wheatstone bridges, photo-electric elements in said circuit forming legs in said Wheatstone bridges, a master photo-sensing unit including photo-electric elements forming one of the legs in said Wheatstone bridges, a key photo-sensing unit including mating photo-electric elements forming the other of said legs in said Wheatstone bridges, a source of radiation in each of said units, a master card and a key card having identical light filtering portions impervious and pervious to radiation defining a code received in their respective unit controlling the impingememnt of radiation on said pl1oto--electric elements, an output circuit connected to said balanced circuit receiving a signal in accordance with a comparative current conductance in said bridges, actuating means connected to said output circuit for selectively and alternatively indicating the identity or lack of identity of codes of said master and said key cards.

6. An electronic locking system comprising, a plurality of balanced bridge circuits, a pair of photo-electric elements forming the first two legs in each of said bridge circuits, a pair of solenoids forming the second two legs in each of said bridge circuits with each solenoid connected in series with a mating photo-electric element; a master photo-sensing unit including photo-electric elements forming one of said first two legs of each of said bridge circuits and means directing radiation toward said photoelectric elements, a key photo-sensing unit including photo-electric elements forming the other of said first two legs of each of said bridge circuits and means directing radiation towards said photo-electric elements, a bank of pairs of switches connected to energizing means with the first switch of each pair operated by a solenoid connected to a photo-electric element in the master unit and the second switch of each pair operated by a solenoid connected to a photo-electric element in said key photo-sensing unit, an output circuit connected through said bank of switches to operate a locking means when said bridge circuits provide a balance output, a master code card received in said master photo-sensing unit having elemental areas defining a code controlling radiation on said photo-electric elements, a key code card received in said key photo-sensing unit having elemental areas defining a code identical with the master and controlling radiation on said photo-electric elements to thereby provide a balanced circuit condition in said bridge circuits.

References Cited by the Examiner UNITED STATES PATENTS 2,266,779 12/1941 Loughridge et al. 340l49 2,320,338 6/1943 Bryce 250-208 X 2,497,405 2/ 1950 Glover.

2,539,043 1/1951 Verneaux 340149 2,714,201 7/1955 Whitehead 340-149 2,842,672 7/1958 Thomsen 250-210 X 2,914,746 11/1959 James 340-449 2,979,695 4/ 1961 Tyrlick et a1. 340-146.2 3,029,345 4/1962 Douglas 250-210 X 3,045,364 7/1962 Surber 340-149 X NEIL C. READ, Primary Examiner.

P. XIARHOS, Assistant Examiner. 

5. A LOCKING SYSTEM COMPRISING, AN ELECTRICALLY BALANCED CIRCUIT INCLUDING, A PLURALITY OF WHEATSTONE BRIDGES, PHOTO-ELECTRIC ELEMENTS IN SAID CIRCUIT FORMING LEGS IN SAID WHEATSTONE BRIDGES, A MASTER PHOTO-SENSING UNIT INCLUDING PHOTO-ELECTRIC ELEMENTS FORMING ONE OF THE LEGS IN SAID WHEATSTONE BRIDGES, A KEY PHOTO-SENSING UNIT INCLUDING MATING PHOTO-ELECTRIC ELEMENTS FORMING THE OTHER OF SAID LEGS IN SAID WHEATSTONE BRIDGES, A SOURCE OF RADIATION IN EACH OF SAID UNITS, A MASTER CARD AND A KEY CARD HAVING IDENTICAL LIGHT FILTERING PORTIONS IMPERVIOUS AND PERVIOUS TO RADIATION DEFINING A CODE RECEIVED IN THEIR RESPECTIVE UNIT CONTROLLING THE IMPINGEMENT OF RADIATION ON SAID PHOTO-ELECTRIC ELEMENTS, AN OUTPUT CIRCUIT CONNECTED TO SAID BALANCED CIRCUIT RECEIVING A SIGNAL IN ACCORDANCE-WITH A COMPARATIVE CURRENT CONDUCTANCE IN SAID BRIDGES, ACTUATING MEANS CONNECTED TO SAID OUTPUT CIRCUIT FOR SELECTIVELY AND ALTERNATIVELY INDICATING THE IDENTITY OR LACK OF IDENTITY OF CODES OF SAID MASTER AND SAID KEY CARDS.
 6. AN ELECTRONIC LOCKING SYSTEM COMPRISING, A PLURALITY OF BALANCED BRIDGE CIRCUITS, A PAIR OF PHOTO-ELECTRIC ELEMENTS FORMING THE FIRST TWO LEGS IN EACH OF SAID BRIDGE CIRCUITS, A PAIR OF SOLENOIDS FORMING THE SECOND TWO LEGS IN EACH OF SAID BRIDGE CIRCUITS WITH EACH SOLENOID CONNECTED IN SERIES WITH A MATING PHOTO-ELECTRIC ELEMENT; A MASTER PHOTO-SENSING UNIT INCLUDING PHOTO-ELECTRIC ELEMENTS FORMING ONE OF SAID FIRST TWO LEGS OF EACH OF SAID BRIDGE CIRCUITS AND MEANS DIRECTING RADIATION TOWARD SAID PHOTO-ELECTRIC ELEMENTS, A KEY PHOTO-SENSING UNIT INCLUDING PHOTO-ELEC- 